• Western hemlock (Tsuga heterophylla) (TSHT):
characteristic density ~380 kg/m3, characteristic strength
~18 N/mm2, mean stiffness ~8 kN/mm2
• Western red cedar (Thuja plicata) (THPL): characteristic
density ~320 kg/m3, characteristic strength ~16 N/mm2,
mean stiffness ~7 kN/mm2.
This makes these species roughly similar to Sitka in grading
terms, although the stiffness of western red cedar is likely to
be too low for good grading yields.
Napier is currently researching some other likely conifer
species for diversification:
• Serbian spruce (Picea omorika)
• Pacific silver fir (or amabilis fir) (Abies amabilis) (ABAM)
• Japanese incense cedar (or sugi / Japanese red cedar)
(Cryptomeria japonica) (CYJP)
• Grand fir (Abies grandis) (ABGR)
• European silver fir (Abies alba) (ABAL).
These minor species constitute only a small proportion of
the home-grown timber resource but could possibly become
a minor component of an existing species combination such
as ‘British spruce’. So long as the aspects of the timber
that are important to manufacturing and construction are
similar enough, the actual botanical species or genus is of
little relevance to the user, especially considering the within
species variability that is already addressed by grading.

Hardwoods
The available volumes of hardwood in the near future
are very limited compared to the conifers, but Napier is
researching sycamore (Acer pseudoplatanus) (ACPS)
and birch (Betula pendula/pubescens) (BTXX), which
have potential for an eight-fold and a 13-fold increase in
available volume respectively by 2045.6 Old visual grading
assignments exist for BS 5756 that assign European oak
(Quercus petraeaand robur) (QCXE) to D24, D30 and D40,
and sweet chestnut (Castanea sativa) (CTST) to D24.

Wider variety needed
The changing focus of British forestry, and the increasing
demands on wood fibre for energy and as a feedstock for
new materials in the desired future bio-based economy,
make it inevitable that the timber industry will widen its
focus from the present small number of commercial
species. The good news is that this does not necessarily
lead to significant changes for the end user. It is, after all,
the performance of the timber that matters and not the
appearance of the tree it came from. n
www.trada.co.uk

About the author

Daniel Ridley-Ellis
Head of the Centre for Wood Science and Technology
Edinburgh Napier University